This invention relates to a Lame mode quartz crystal resonator including a quartz crystal obtained by cutting out a blank quartz crystal along particular planes, and more particularly to a Lame mode quartz crystal resonator most suitable as a reference signal source for use in portable instruments such as IC cards strongly required to be miniaturized, to operate with high accuracy and to be manufactured inexpensively.
An outline of Lame mode quartz crystal reson Resonators and Devicesxe2x80x9d which is a thesis written b application in the Transaction of xe2x80x9cthe Institute of Communication Engineersxe2x80x9d, vol. J82-C-I, No. 12 (December 1999), pages 667 to 682.
FIG. 7 illustrates well-known cutting directions of a quartz crystal structure of a Lame mode quartz crystal resonator with respect to the coordinate system o-xyz of the crystal structure. In the drawing, axes xxe2x80x2, yxe2x80x2, zxe2x80x2 and zxe2x80x3 are coordinate axes after the coordinate system has been rotated (crystal axes after being cut). The cutting directions are obtained by rotating a Y-plate quartz crystal through an angle of xcfx86y about the x-axis and then rotating the Y-plate quartz crystal through an angle of xcex8y about the new axis yxe2x80x2 corresponding to the y-axis produced by the rotation about the x-axis.
FIG. 8 illustrates a relation between the cut angles xcfx86y and xcex8y of the quartz crystal for the Lame mode quartz crystal resonator of the prior art, giving a zero temperature coefficient. As shown in the curve 102, the cutting angle xcex8y of the Lame mode quartz crystal resonator of the prior art exists within 30xc2x0 to 60xc2x0.
FIG. 9 illustrates the relation between the cutting angle xcex8y and the second order temperature coefficient xcex2 with the cutting angle xcex8y being within the range in FIG. 8. As shown in the curve 103 in FIG. 9, when the cutting angle xcex8y is 45xc2x0, the second order temperature coefficient xcex2 is xe2x88x925.4xc3x9710xe2x88x928/xc2x0 C.2 whose absolute value is very large. As the cutting angle xcex8y varies from 45xc2x0, the absolute value of the second order temperature coefficient xcex2 becomes smaller as shown in the curve 103 in FIG. 9. At the cutting angle xcex8y of 30xc2x0 or 60xc2x0, xcex2 becomes xe2x88x924.5xc3x9710xe2x88x928/xc2x0 C.2.
FIG. 20 illustrates a Lame mode quartz crystal resonator using the quartz crystal 200 of the prior art described above, which includes a vibrating portion 207, supporting frames 201 and 213 and a mounting portion 202. Disposed on the vibrating portion 207 are electrodes 208, 209 and 210, which have electrode terminals 211 and 212 at the mounting portions 202. (Also disposed on the rear side of the vibrating portion are electrodes, which are not visible in FIG. 20.) Among these electrodes, two electrodes adjacent each other on the same side or two electrodes positioned aligned on front and rear sides form the different polarity. Moreover, the vibrating portion 207 is connected through connecting portions 203 and 206 to the supporting frames 213 and 201 and connected through connecting portions 204 and 205 to the supporting frames 213 and 201 and the mounting portion 202.
With this arrangement, however, as such a quartz crystal has the very large second order temperature coefficient xcex2 described above, it would be impossible to obtain a Lame mode quartz crystal resonator having less frequency change over a wide temperature range. Accordingly, there has been a remaining problem to be solved to realize a Lame mode quartz crystal resonator having a smaller second order temperature coefficient xcex2.
Moreover, as the Lame mode quartz crystal resonator of the prior art includes the vibrating portion connected through the connecting portions at its four ends to the supporting frames and the mounting portion described above, the vibrating portion suffers from increased energy losses upon vibrating, as a result of which its series resistance R1 increases and quality factor Q decreases as remaining problems to be solved. Consequently, it has been expected to provide a novel Lame mode quartz crystal resonator minimizing the energy losses at a vibrating portion.
It is an object of the invention to provide an improved Lame mode quartz crystal resonator which eliminates all the disadvantages of the prior art described above and which has small second order temperature coefficient xcex2 and is adapted to minimize energy losses at its vibrating portion leading to lower series resistance R1 higher quality factor Q.
In order to accomplish this object, the Lame mode quartz crystal resonator vibrating in two vibrations in different phases according to the invention is formed of an X-plate quartz crystal obtained in a manner that a blank X-plate quartz crystal having a coordinate system consisting of x, y and z axes is rotated through 36.5xc2x0 to 47xc2x0 about its y-axis and further rotated through 65xc2x0 to 85xc2x0 about a new xxe2x80x2-axis corresponding to said x-axis produced by said rotation about said y-axis, and the thus rotated blank X-plate quartz crystal is then cut out along planes parallel to x-y, y-z and z-x planes of the original coordinate system, respectively.
In another aspect of the invention, the Lame mode quartz crystal resonator vibrating in overtone mode includes a vibrating portion, a supporting frame and a mounting portion formed integrally, and the vibrating portion is connected through two connecting portions to the supporting frame and the mounting portion.
In this manner, the invention provides the Lame mode quartz crystal resonator using the quartz crystal cut in a novel fashion exhibits a small second order temperature coefficient xcex2, and owing to the two connecting portions for connecting the vibrating portion and supporting frame, a micro-miniature Lame mode quartz crystal resonator can be obtained which has less vibrational energy losses at the vibrating portion and a smaller series resistance R1.
The overtone Lame mode quartz crystal resonator having the quartz crystal cut in the novel manner has following significant effects.
(1) With the overtone Lame mode quartz crystal resonator according to the invention, the second order temperature coefficient xcex2 is xe2x88x921xc3x9710xe2x88x928/xc2x0 C.2 whose absolute value is very small. Therefore, the invention can provide a Lame mode quartz crystal resonator whose frequency change is minimized over a wide temperature range.
(2) According to the invention, two connecting portions are provided for connecting the vibrating portion and the support frame, thereby minimizing the vibrational energy losses, as a result of which a Lame mode quartz crystal resonator having a lower series resistance Q1 and a high quality factor Q can be obtained.
(3) According to the invention it is possible to form integrally the vibrating portion, the supporting frame, the mounting portion and the connecting portions so that a quartz crystal resonator can be realized which is miniaturized, inexpensive and beneficial to mass production because a number of resonators on a quartz crystal wafer can be simultaneously treated in a batch.
(4) The invention can produce the quartz crystal resonator formed integrally by the chemical etching process so that a Lame mode quartz crystal resonator can be realized which is superior in shock resistance.
The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.